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Bayou-Diversity (18 March 2018) Few people in Maine, Wyoming or California can relate to the term "backwater" like those who live in Louisiana. It refers to the natural, cyclic overflow of rivers and bayous that inundates areas characterized by bottomland hardwood vegetation. Backwater generally occurs in winter or spring in response to heavy, seasonal precipitation on local watersheds or as far away as the upper tributaries of the Mississippi River. The key word in this definition is "natural" because backwater has created much of the land that we know here and continues to shape the flora and fauna.

Backwater dictates the type of plants that grow in overflow areas by replenishing shallow water tables to insure that only species adapted to live in wetlands can survive. Pine seedlings frequently invade swamps during dry cycles only to be killed when the floods return. The rising and falling waters disperse floating fruits and seeds of mayhaw, overcup oak, water hickory, and cypress to provide diversity throughout the ecosystem.

From longnose gar to largemouth bass, backwater is the key to many fisheries by providing critical spawning habitat. Backwater allows the temporary passage of fish from one oxbow lake to another, again ensuring diversity down to the genetic level. Native terrestrial wildlife have adapted to the floods, routinely following the water in and out of the swamps. Slowly rising waters cause few problems for most species if suitable habitat is available in nearby uplands. Deer along the Mississippi River give birth to fawns up to two months later than those in nearby hills, perhaps to avoid backwater at a critical time.

The most important function of backwater is likely the infusion of nutrients to fuel the system from the bottom up. Several hundred thousand acres of former backwater areas in Louisiana never or rarely flood because of levees, ditches, pumps and dams. Most have been converted to agriculture. Even in remaining forested areas the cycle is broken, and the land is never as productive. Nutrient deficient plants eventually produce less fruit, acorns, and browse, lowering the carrying capacity of the deer herd. Lack of flooding results in fewer fish and crawfish to support great blue herons, raccoons and otters. The absence of backwater means less seed and animal dispersal and thus less diversity. When diversity decreases to a finite point, ecosystems often implode and cease to exist as a sustainable unit.

For thousands of years humans adapted to backwater and even exploited its benefits without altering the natural phenomenon. Only in the last hundred years has man developed the tools to change the environment of Louisiana at a landscape level. At some levels in some areas we may be progress poor. (adapted from Bayou-Diversity: Nature & People in the Louisiana Bayou Country, LSU Press)


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